The Gentleman Magazine Issue 20 | April 2020 | Page 49

FUNCTION MODES
The internal combustion engine and electric motors work in
synergy to generate an incredible 1,000 cv, which puts the SF90
Stradale at the very top of the range in performance terms. The
control logic optimally manages the power flows either with
the emphasis on efficiency or performance depending on the
user profile selected by the driver.
Thanks to an additional steering wheel-mounted selector,
dubbed the eManettino (analogous to the Manettino which is
used to set the electronic vehicle dynamics modes), the driver
can choose from four different power unit management modes:
eDrive: the internal combustion engine remains off and
traction is entrusted entirely to the electric front axle. Starting
with a fully charged battery, the car can cover up to 25 km in
this mode. This mode is ideal for city centre driving or any
other situation in which the driver wishes to eliminate the
sound of the Ferrari V8.
Hybrid: this is the default setting when the car is turned on,
in which the power flows are managed to optimise the overall
efficiency of the system. The control logic autonomously decides
whether to keep the internal combustion engine running or
turn it off. If it is on, the internal combustion engine can run
at maximum power thus guaranteeing powerful performance
whenever the driver requires.
Performance: unlike ‘Hybrid’, this mode keeps the ICE running
because the priority is more on charging the battery than on
efficiency. This guarantees that power is instantly and fully
available when required. This mode is best suited to situations
in which driving pleasure and fun behind the wheel are the
main focus.
Qualify: this mode allows the system to achieve maximum
power output by allowing the electric motors to work at their
maximum potential (162kW). The control logic prioritises
performance over battery charging.
VEHICLE DYNAMICS
The exceptional work done to boost the power unit’s power
would have all been in vain without in-depth dynamics
research and the development of a whole series of solutions
to boost the SF90 Stradale’s lap times, whilst simultaneously
guaranteeing that drivers of all kinds could make full use of the
car’s potential and have fun behind the wheel.
The new hybrid architecture required extensive and lengthy
integration work on the car’s many different control logics. The
three areas concerned are: the high-voltage system controls
(battery, RAC-e, MGUK, inverter), engine and gearbox control
and vehicle dynamics controls (traction, braking, Torque
Vectoring).
Integrating these areas with the existing vehicle control logics
led to the development of the new eSSC (electronic Side Slip
Control) vehicle control system. The eSSC introduces three
innovative dynamic regulation and distribution strategies for
engine torque to all four wheels:
- Electric Traction Control (eTC): optimally manages the
availability of the torque – both ICE and electric – distributing
it to the individual wheels to suit driving conditions and grip
requirements
- brake-by-wire control with ABS/EBD: allows the braking
torque to be split between the hydraulic system and the electric
motors (brake torque blending), allowing regenerative recovery
under braking which actually boosts performance and brake
feel rather than compromising them
- Torque Vectoring: available on the front axle to manage
electric traction on outside and inside wheel in cornering to
maximise traction exiting the corner and help ensure easy,
confident, high-performance driving.
Longitudinal dynamics
Thanks to the introduction of the RAC-e electric axle and
traction control, eTC (Electronic Traction Control), on all
four wheels, it is now possible to exploit the additional grip
offered by the front wheels when accelerating. Improved
overall grip combined with the improved power delivery from
the electric motors at low speeds, has significantly improved
the SF90 Stradale’s longitudinal acceleration, making it the new
benchmark for standing starts.
Even at high speeds and in higher gears, the combined
contribution of the electric motors in maximum traction
conditions helps reduce ICE response times, significantly
improving longitudinal acceleration and thus performance.
The new brake-by-wire system manages kinetic energy recovery
through the electric motors by implementing electronically-
controlled blending of hydraulic and electric braking, entirely
unnoticed by the driver. Under normal braking conditions,
energy recovery using the electric motors is the priority. The
hydraulic system intervenes to support the electric one under
hard braking.
Lateral dynamics
The eSSC control logic also supervises how torque is distributed
between the front wheels using the RAC-e motors and the
electronic control derived from the Torque Vectoring concept,
varying between the inside and the outside wheel in cornering
based on dynamic conditions with the aim of maximising
performance and delivering easier handling.
CHASSIS
Although the extra 270 kg required to incorporate the hybrid
system into the car have been amply offset by the extra power
delivery (220 cv, with a weight/power ratio for the system alone
of 1.23 kg/cv), in-depth research was still required to ensure
that overall weight was kept to 1,570 kg, thus guaranteeing a
record-breaking weight/power ratio of 1.57 kg/cv.
The chassis has been completely redesigned with a multi-
material and multi-technology approach to absorb the
extra stresses associated with the new power unit and the
introduction of AWD. A number of technological innovations
have been introduced, not least hollow castings, which replace
the traditional ribbed castings. Other new solutions include an
all-carbon-fibre bulkhead between the cabin and the engine
and two new aluminium alloys, one of which is a high-strength
7000 series alloy for some of the sheet metal. As a result, the
SF90 Stradale chassis boasts 20% higher bending stiffness and
40% higher torsional rigidity than previous platforms without
any increase in weight. This has significant advantages for the
car’s dynamics.
The Gentleman Magazine | 49